In recent years, muscle atrophy has become a major problem in association with acceleration of aging and insufficient exercise due to progress in transportation. Muscle atrophy means that a muscle mass and muscular strength are decreased. In general, it is said that a muscle mass and muscular strength are decreased from about 40 years old and many elderly people are in the state of sarcopenia, specifically age-related sarcopenia. Sarcopenia mainly means a decrease in a muscle mass and muscular strength due to aging and is important element of locomotive syndrome and frailty, and it is pointed out that a care need becomes required due to sarcopenia. Locomotive syndrome is referred to as exerciser syndrome, and is an important factor of being in a state of high risk of getting nursing care or becoming a condition to require nursing care by deterioration of mobility function due to a disability of a locomotor apparatus such as muscle, bone, joint, cartilage and intervertebral disc. Frailty means a condition in which muscular strength, mental vitality and physical vitality are deteriorated. Thus, the decrease in a muscle mass and muscular strength lowers not only quality of life (QOL) but also activities of daily living, and closely relates to the occurrence of complications and a greater care burden. In the United States, the decrease in a muscle mass and muscular strength are in the top five health risks, and the related medical expenses are estimated to be about 2.5 trillion yen.
Both of adequate nutritional intake and exercise are required for muscle enhancement, namely increase and maintenance of a muscle mass and muscular strength, as well as suppression of the decrease of a muscle mass and muscle weakness. In case of elderly people, however, a food intake amount tends to be decreased due to loss of appetite and a ratio of an absorption amount to nutrient intake amount tends to be lowered due to a decline in swallowing function, saliva amount and digestive system function. In addition, an efficiency of body function to transform an absorbed peptide or amino acid into muscle protein is also decreased. Furthermore, not only elderly people have less access to exercise but also an increasing efficiency of a muscle mass by an exercise is lowered. As a result, for example, when physical activity of elderly people is decreased due to an injury or disease, a muscle mass and muscular strength are further decreased, and elderly people get trapped into a negative cycle of a decline in physical activity and a deterioration in muscle atrophy.
Muscle enhancement is required for improvement in exercise capacity in sports, prevention and relief of obesity and metabolic syndrome, and slimming. Also, muscle enhancement is required for a non-human animal for the purpose of growth promotion, meat increase and meat quality improvement.
In order to enhance muscle, it is necessary to enlarge or maintain the size of the muscle fiber constituting the muscle. A muscle fiber is a multinucleated cell, and the size of the cell is dependent on the number of the nucleus. Thus, it is necessary to increase the number of nucleus in order to enlarge or maintain a muscle fiber, but the nucleus of a muscle fiber does not increase, and a nucleus has to be supplied into a muscle fiber from the outside of the cell. A nucleus is supplied into a muscle fiber by a myosatellite cell, which exists between the basement membrane and the cell membrane of a muscle cell constituting the muscle. A myosatellite cell is also referred to as a satellite cell. A myosatellite cell is usually in a resting state and undifferentiated, but becomes activated to supply a nucleus into a muscle fiber through processes such as proliferation, differentiation and fusion with a muscle fiber due to exercise, muscle damage and growth. Thus, the activation of a myosatellite cell contributes to muscle enhancement.
Since a decline in a muscle mass and muscular strength progresses with aging as described above, such a decline in a muscle mass and muscular strength should be prevented before becoming obvious. In addition, since elderly people have to continue to take an everyday medicine to suppress chronic disease in some cases, a synthetic medicine has a problem of an unpredictable side effect due to the combination with the everyday medicine.
Accordingly, a safe component having a muscle enhancing action has been searched.
For example, Patent document 1 discloses a muscle senescence inhibitor which contains a catechin contained in a tea drink as an active ingredient. Patent document 2 discloses a muscle-enhancing agent which contains the genus Salacia of the family Celastraceae or an extract thereof. A plant of the genus Salacia grows wild in India, Sri Lanka and Southeast Asian countries. It is reported in Non-patent document 1 that leucine, which is a branched chain amino acid, has a muscle protein synthesizing action. Patent Document 3 discloses a satellite cell differentiation promoting agent containing Raphuma, which is a plant of the family Amyorae, or an extract thereof; however, Patent Document 3 merely discloses a differentiation inducing effect on a skeletal muscle-derived cell and does not disclose the activation of a myosatellite cell.
Lemon myrtle is an evergreen tree of Myrtaceae family originating in Australia, and the scientific name thereof is Backhousia citriodora. Lemon myrtle is a kind of herb, contains a lot of citral as an essential oil component, has a strong refreshing aroma, and is used for cooking. Lemon myrtle has been under study. For example, Patent documents 4 to 6 respectively discloses a whitening composition having a tyrosinase inhibitory action, a skin fibroblast cell growth-promoting agent to prevent or relieve a skin problem due to ultraviolet rays or the like, advanced glycation end products formation inhibitor for preventing or relieving diabetes or diabetes complication which contain lemon myrtle or an extract thereof. On the one hand, an effect of lemon myrtle on muscle has not been studied.